Effects of lime and oxalic acid on antioxidant enzymes and active components of Panax notoginseng under cadmium stress

Contents of Cd and Ca in Panax notogensing roots

The Ca content of P. notoginseng roots increased significantly with the increase of lime application rates under the same concentration of oxalic acid sprayed on leaves (Table 2). Compared with no lime application, the Ca content was the highest increased by 212% under 3750 kg hm⁻² lime without spraying oxalic acid. The content of Ca slightly increased with the increase of oxalic acid spraying concentrations under the same rate of lime application.

The contents of Cd in roots ranged from 0.22 to 0.70 mg kg⁻¹. The content of 2250 kg hm⁻² Cd decreased greatly with the increase of lime application rates under the same spraying concentration of oxalic acid. Compared with the control, the root Cd contents decreased by 68.57% under the application of 2250 kg hm⁻² lime and 0.1 mol L⁻¹ oxalic acid spraying. The Cd contents of P. notoginseng roots decreased significantly with the increase of oxalic acid spraying concentrations under application of non-lime and 750 kg hm⁻² lime. The root Cd contents decreased at first and then increased with the increase of oxalic acid concentrations under the application of 2250 kg hm⁻² lime and 3750 kg hm⁻² lime. In addition, the Bivariate analysis showed that the Ca content of P. notoginseng roots was significantly affected by lime (F = 82.84**), and the Cd content of P. notoginseng roots was significantly affected by lime (F = 74.99**) and oxalic acid (F = 7.72*).

MDA contents and relative antioxidase activities

The content of MDA decreased greatly with the increase of the rates of lime application and oxalic acid spraying concentrations. There was no significant difference in the content of MDA in the roots of P. notoginseng with non-lime and 3750 kg hm⁻² lime application. Under 750 kg hm⁻², 2250 kg hm⁻² lime application, the MDA content with 0.2 mol L⁻¹ oxalic acid spraying concentration treatment decreased by 58.38% and 40.21% comparing with non-oxalic acid spraying application, respectively. The content of MDA (7.57 nmol g⁻¹) was the lowest under 750 kg hm⁻² lime application and 0.2 mol L⁻¹ oxalic acid spraying treatment (Fig. 1).

There was no significant difference in SOD activity in the roots of P. notoginseng except for the application rate of 3750 kg hm⁻² lime. Under 0, 750 and 2250 kg hm⁻² lime application, the SOD activities of 0.2 mol L⁻¹ oxalic acid spraying treatment were significantly higher than that without oxalic acid application, which increased by 177.89%, 61.62% and 45.08%, respectively. The SOD activity (598.18 U g⁻¹) in roots was the highest non-lime application and 0.2 mol L⁻¹ oxalic acid spraying treatment. The SOD activities increased with the increase of lime application rates with the same concentration of no oxalic acid or 0.1 mol L⁻¹ oxalic acid spraying treatment. The SOD activities decreased significantly with 0.2 mol L⁻¹ oxalic acid spraying treatment (Fig. 2).

The similar as the root SOD activity, the POD activity (63.33 μmol g⁻¹) in the root was the highest with non-lime and 0.2 mol L⁻¹ oxalic acid spraying treatment, which was 148.35% higher than that of the control (25.50 μmol g⁻¹). The POD activity increased at first and then decreased with the increase of oxalic acid spraying concentration and 3750 kg hm⁻² lime application treatment. The POD activity decreased by 36.31% with 0.2 mol L⁻¹ oxalic acid treatment compared with 0.1 mol L⁻¹ oxalic acid treatment (Fig. 2).

The CAT activities were significantly higher than that of the control except for 0.2 mol L⁻¹ oxalic acid spraying and 2250 kg hm⁻² or 3750 kg hm⁻² lime application treatments. The CAT activities of increased by 276.08%, 276.69% and 33.05% with 0.1 mol L⁻¹ oxalic acid spraying and 0, 2250 kg hm⁻² or 3750 kg hm⁻² lime application treatments, respectively, compared with that without oxalic acid spraying. The root CAT activity (803.52 μmoL g⁻¹) was the highest with non-lime and 0.2 mol L⁻¹ oxalic acid treatment. The CAT activity (172.88 μmol g⁻¹) was the lowest with 3750 kg hm⁻² lime and 0.2 mol L⁻¹ oxalic acid treatment (Fig. 2).

Bivariate analysis showed that the CAT activity and MDA of P. notoginseng roots was significantly relationship with the amount of oxalic acid spraying or lime application and both treatment (Table 3). The root SOD activity was significantly relationship with both of lime and oxalic acid treatment or oxalic acid spraying concentration. The activity of POD in roots was significantly relationship with the lime application rate or both of lime and oxalic acid treatment.

Contents of medicals components

Contents of soluble sugar and soluble protein

The content of soluble sugar in roots decreased with the increase of the rate of lime application and oxalic acid spraying concentration. There was no significant difference in the content of soluble sugar in the roots of P. notoginseng under without lime and 750 kg hm⁻² lime application. Under 2250 kg hm⁻² lime application, the soluble sugar content with 0.2 mol L⁻¹ oxalic acid treatment was significantly higher than that of non-oxalic acid spraying, which increased by 22.81%. Under the application of lime 3750 kg hm⁻², the soluble sugar content decreased significantly with the increase of oxalic acid spraying concentration. The soluble sugar content with 0.2 mol L⁻¹ oxalic acid spraying treatment decreased by 38.77% compared with that of non-oxalic acid spraying. Moreover, the soluble sugar content with 0.2 mol L⁻¹ oxalic acid spraying treatment was the lowest, which was 205.80 mg g⁻¹ (Fig. 3).

The content of soluble protein in roots decreased with the increase of the amount of lime application and oxalic acid spraying treatment. In the absence of lime, the soluble protein content with 0.2 mol L⁻¹ oxalic acid spraying treatment was significantly lower 16.20% than that of the control. Under 750 kg hm⁻² lime application, there was no significant difference in the content of soluble protein in the roots of P. notoginseng. Under 2250 kg hm⁻² lime application, the soluble protein content with 0.2 mol L⁻¹ oxalic acid spraying treatment was significantly higher 35.11% than that of non-oxalic acid spraying. Under the application of lime 3750 kg hm⁻², the soluble protein content decreased significantly with the increase of oxalic acid spraying concentration, and the soluble protein content (269.84 μg g⁻¹) was the lowest under 0.2 mol L⁻¹ oxalic acid spraying treatment (Fig. 3).

Contents of free amino acid and proline

There was no significant difference in the content of free amino acid in the roots of P. notoginseng under without lime application. The content of free amino acid decreased at first and then increased with the increase of oxalic acid spraying concentrations and 750 kg hm⁻² lime application. The content of free amino acid significantly increased by 33.58% with 2250 kg hm⁻² lime application and 0.2 mol L⁻¹ oxalic acid spraying treatment compared with non-oxalic acid spraying treatment. The content of free amino acid decreased significantly with the increase of the concentration of oxalic acid spraying and the application of 3750 kg hm⁻² lime. The content of free amino acid with 0.2 mol L⁻¹ oxalic acid spraying treatment decreased by 49.76% compared with that without oxalic acid spraying treatment. The content of free amino acid reached the highest under without oxalic acid spraying treatment, which was 2.09 mg g⁻¹. The content of free amino acid (1.05 mg g⁻¹) with 0.2 mol L⁻¹ oxalic acid spraying treatment was the lowest (Fig. 4).

The content of proline in roots decreased with the increase of the amount of lime application and oxalic acid spraying treatment. There was no significant difference in the proline content of P. notoginseng root under non-lime application. The proline content decreased at first and then increased with the increase of oxalic acid spraying concentration and 750 or 2250 kg hm⁻² lime application. The proline content with 0.2 mol L⁻¹ oxalic acid spraying treatment was significantly higher than that of 0.1 mol L⁻¹ oxalic acid spraying treatment, which increased by 19.52% and 44.33%, respectively. Under the application of 3750 kg hm⁻² lime, the content of proline decreased significantly with the increase of oxalic acid spraying concentrations. The content of proline with 0.2 mol L⁻¹ oxalic acid spraying decreased by 54.68% compared with that without oxalic acid. The content of proline was the lowest under 0.2 mol L⁻¹ oxalic acid treatment, which was 11.37 μg g⁻¹ (Fig. 4).

Contents of saponins

The contents of P. notoginseng saponins was Rg1 > Rb1 > R1. The contents of the three saponins had no significant difference with increase of the concentrations of oxalic acid spraying and no application of lime (Table 4).

The contents of R1 with 0.2 mol L⁻¹ oxalic acid spraying was significantly lower than that without oxalic acid spraying and rates of 750 or 3750 kg hm⁻² lime application. Under the concentration of 0 or 0.1 mol L⁻¹ oxalic acid spraying, there was no significant difference in contents of R1 with increase of rates of lime application. Under the concentration of 0.2 mol L⁻¹ oxalic acid spraying, the contents of R1 with 3750 kg hm⁻² lime was significantly lower 43.84% than that without lime application (Table 4).

The contents of Rg1 increased at first and then decreased with the increase of oxalic acid spraying concentrations and 750 kg hm⁻² lime application. Under the application rates of 2250 or 3750 kg hm⁻² lime, the contents of Rg1 decreased with the increase of oxalic acid spraying concentration. With the same concentration of oxalic acid spraying, the Rg1 content increased at first and then decreased with the increase of lime application rates. Compared with the control, except that the Rg1 content with three concentrations of oxalic acid spraying and 750 kg hm⁻² lime was higher than that of the control, the contents of Rg1 in the roots of P. notoginseng under other treatments was lower than that of the control. The Rg1 content was the highest with 750 kg hm⁻² lime and 0.1 mol L⁻¹ oxalic acid spraying treatment, which was higher 11.54% than that of the control (Table 4).

The contents of Rb1 increased first and then decreased with the increase of oxalic acid spraying concentration and 2250 kg hm⁻² lime application. The content of Rb1 with 0.1 mol L⁻¹ oxalic acid spraying reached the maximum value of 3.46%, which was higher 74.75% than that without oxalic acid spraying treatment. Under other lime application treatments, there was no significant difference among different oxalic acid spraying concentrations. With 0.1 and 0.2 mol L⁻¹ oxalic acid spraying treatments, the contents of Rb1 decreased at first and then decreased with the increase of lime application rates (Table 4).

Contents of flavonoids

With the same concentration of oxalic acid spraying, the content of flavonoids increased at first and then decreased with the increase of the amounts of lime application. There was no significant difference in the content of flavonoids under different concentrations of oxalic acid spraying without the application of lime or 3750 kg hm⁻² lime. Under 750 and 2250 kg hm⁻² lime application, the content of flavonoids increased at first and then decreased with the increase of the concentration of oxalic acid spraying. Under the treatment of 750 kg hm⁻² application and 0.1 mol L⁻¹ oxalic acid spraying, the content of flavonoids was the highest, which was 4.38 mg g⁻¹, which was higher 18.38% than that of the same rate of lime application and without spraying oxalic acid. The content of flavonoids with 0.1 mol L⁻¹ oxalic acid spraying treatment increased by 21.74% compared with that without oxalic acid spraying treatment and 2250 kg hm⁻² lime application (Fig. 5).

Bivariate analysis showed that the content of soluble sugar in P. notoginseng root was significantly relationship with the amount of lime application and the concentration of oxalic acid spraying. The content of soluble protein in root was significantly relationship with lime application rates, both of lime and oxalic acid. The contents of free amino acid and proline in roots were significantly relationship with lime application rates, oxalic acid spraying concentrations, both of lime and oxalic acid (Table 5).

The content of R1 in the root of P. notoginseng was significantly relationship with oxalic acid spraying concentrations, lime application rates, both of lime and oxalic acid. The content of flavonoids was significantly relationship with oxalic acid spraying concentrations, lime application rates.

Source: Ecology - nature.com